The Comparative Pathology Core A will provide centralized pathology support for the three scientific projects and represents an evolution from the Mouse Pathobiology Core from the initial grant cycle. A major goal of the Comparative Pathology Core will be to provide expertise in mouse and human pathology with up-to-date proficiency in mammary gland and breast cancer pathology. In addition, a DVM, PhD postdoc in mouse pathology will perform the mouse necropsies (autopsies), cutting and processing of tissues, and evaluation of histopathology and special stains under the supervision of faculty pathologists. This will ensure excellence and continuity of service for the research projects. The Core will have 6 personnel that include three pathologists (one medical and two veterinary), medical oncologist (breast cancer specialist), a pathology fellow, and part-time histology technician. The Comparative Pathology Core is essential to ensure integration of the specific aims and experiments in relation to translation of the mouse genetic models to human breast cancer. The three pathologists and oncologist have a long track record of working together on collaborative projects, and therefore are well positioned to provide support for Core A. In addition, all three pathologists and the oncologist have collaborated with Drs. Ostrowski and Leone leading to shared authorship on manuscripts with high impact on mammary cancer microenvironment and its relationship to mammary cancer progression (1, 2). Facilities will include four necropsy rooms (including one devoted to mouse pathology), tissue processing facilities, histology laboratory with four full-time technicians (one devoted to the Core) and an automated Dako immunostainer. In Situ Molecular Pathology Core Lab with a Ventana staining system and NUANCE PLUS InForm computer-based analyses of co-expression of molecular targets, microscopy facilities including a 10-headed microscope with video output for conferences, laser capture microdissection facility and staff, tissue microarray laboratory, mouse imaging facilities including high resolution ultrasound, digital gross and microscopic photography, histomorphometry equipment including a fluorescent microscope and Image Pro Plus analysis software, and mouse surgery facilities. A SharePoint website will facilitate data transfer and sharing between the cores and project staff. These faculty and services will provide a unique resource to the research projects and significantly enhance the quality and validity of the research data.